Polymeric nanocomposites are produced to enhance material performance or to achieve functional properties such as electrical, thermal, barrier and antimicrobial compared to conventional polymeric composites. Polymeric nanocomposites are a new class of materials that contain an organic polymer and inorganic particles dispersed at nanoscale (1-100 nm) within the polymeric matrix. Specifically, polymeric nanocomposites based on layered phyllosilicates have been used extensively in industry since they show significant property enhancement compared to those of pure polymer or conventional filled polymeric composites.
Particularly, elastomeric nanocomposites containing phyllosilicate clay provide improvements in properties such as mechanical, electrical and thermal. In addition, new functionality such as improved barrier and flame retardant properties may also be introduced to the elastomeric compound. Generally, phyllosilicate clay is converted into organophilic clay by intercalating organic molecules, preferably tertiary alkyl ammonium ions, since hydrophilic clays are not in general compatible with elastomers.
Elastomeric nanocomposites are prepared by polymerizing, in situ, the elastomeric monomer in the presence of organophilic phyllosilicate clays or by intercalating the elastomer into clay in solution or by direct melt mixing the elastomer in the presence of clay. As most elastomers including natural rubber (NR) are available in the solid or latex form, intercalation of layered silicates either by direct melt mixing with dry rubber or in solution are industrially feasible techniques and are used to prepare rubber nanocomposites that contain phyllosilicate clays that are exfoliated or separated. Exfoliation of layered silicates into individual layers or platelets with 1 nm thickness and dispersion of them homogeneously in the rubber matrix, gives rise to the rubber-layered silicate nanocomposites. The degree of exfoliation significantly affects the material properties.
Depending on the dispersion of layered phyllosilicates in the rubber matrix, rubber-layered silicate nanocomposites can be categorized into two ideal structures: intercalated or exfoliated. When rubber intercalates into the interlayer spacing of the clay resulting in an alternating elastomer and clay structure, it gives rise intercalated nanocomposites. In an exfoliated nanocomposite structure, elastomer intercalates or diffuses into the layered silicates. The clay particles are then separated into their primary platelets, where individual clay layers are of 1 nm thickness, and dispersed uniformly in a continuous elastomer matrix. Since exfoliation of the clay is the key factor in the enhancement of properties, various exfoliation techniques have been developed to prepare rubber nanocomposites containing layered phyllosilicates.
WO/2008/068543 discloses production of elastomeric nanocomposites containing organophilic nanoclay and carbon black, in which organically modified nanoclay is melt mixed with elastomers. WO/2008/045029 discloses exfoliated clay nanocomposites of star branched elastomer. US 2005/0277723 discloses clay elastomer nanocomposites, and functionalized carboxylic acid or ester groups having pendant elastomer units for improved air barrier properties of tire liners. US 2003/0191224 disclose nanocomposites for tire liner compositions containing organically modified clay having an ammonium group and an amino group. US 1998/5807629 discloses an elastomer/layered material nanocomposite with low air permeability to be used as a tire liner, wherein the nanocomposite was obtained by dispersing a layered material in an elastomer containing functionalized copolymer of isobutylene and isoprene.
US 2004/6759464 discloses a nanocomposite functionalized elastomeric polymer which is pre-intercalated or partially exfoliated with clay in an aqueous medium. Aqueous dispersions of the elastomer and the clay were used to form nanocomposites containing reinforcing agents. US1999/5973053 discloses nanocomposites that are formed by making clay composite intercalated with an onium ion and an organic molecule having a polar group clay composite material is mixed with a rubber material rubber nanocomposite is formed by solvent or melt-mixing methods.
Given the above, it would be advantageous to have a melt mixing method to produce exfoliated nanocomposites for property enhancement while reducing the cost by including inert fillers.
Particularly the increase in tensile strength and modulus by using melt mixing without the use of solvents are desirable in terms of manufacturing ease.